Receiving device and integrated circuit for reception

ABSTRACT

In order to improve various characteristics of a receiving circuit for digital radio services, circuits are provided for forming two local oscillation signals, whose frequencies are both the center frequency between a first ensemble and a second ensemble, and whose phases differ by 90° from each other. Furthermore, there are provided mixer circuits for frequency-converting the received signal into intermediate frequency signals in accordance with the local oscillation signals, phase-shift circuits to which the intermediate frequency signals are supplied, and an addition/subtraction circuit for performing one of addition and subtraction of the outputs of the phase-shift circuits. In addition, there are provided intermediate frequency filters to which the output signal of the addition/subtraction circuit is supplied and demodulation circuits to which the output signals of the intermediate frequency filters are supplied. By switching the process in the addition/subtraction circuit to addition or subtraction, the signals of the first ensemble and the second ensemble are selectively extracted from the demodulation circuits.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a receiving device and an integratedcircuit for reception.

2. Description of the Related Art

Digital audio radio services in the U.S. are called “DARS”, and in DARS,satellite waves and terrestrial waves are used in combination so thateven a receiver mounted in a mobile unit such as vehicle can reliablyreceive the radio waves.

More specifically, in the DARS, a 2.3 GHz band is used, and as shown inpart B of FIG. 6, two services are broadcast. Currently, each of theservices uses a frequency band of 12.5 MHz. As is also shown in part Aof FIG. 6, one service is formed of two ensembles A and B, and each ofthese ensembles A and B provides 50 channels of programs contents.Therefore, one service provides programs of 100 channels.

The ensemble A is broadcast with individual signals A1, A2, and A3, andthe ensemble B is broadcast with individual signals B1, B2, and B3. Thatis, the contents of the signals A1, A2, and A3 are the same, and thecontents of the signals B1, B2, and B3 are the same. Therefore, if anyone of the signals A1, A2, and A3 can be received, the program of theensemble A can be listened to, and in a similar manner, if any one ofthe signals B1, B2, and B3 can be received, the program of the ensembleB can be listened to.

As is also shown in part A of FIG. 6, the signals A1 to A3 and B1 to B3are arranged as the signals A1, A2, A3, B3, B2, and B1 in order offrequency, and the signals A1, A2, and A3, and the signals B3, B2, andB1 are symmetrically placed about a center frequency fC between thesignal A3 and the signal B3.

The signals A1, A2, B1, and B2 are QPSK (Quadrature Phase Shift Keying)signals. The signals A1 and B1 are transmitted from a broadcastingsatellite BS1 over the Western U.S., and the signals A2 and B2 aretransmitted from a broadcasting satellite BS2 over the Eastern U.S.(strictly speaking, the satellites BS1 and BS2 are positioned along theEquator at longitudes corresponding to the Western U.S. and the EasternU.S.). Also, the signals A3 and B3 are OFDM (Orthogonal FrequencyDivision Multiplex) signals and are transmitted from an antenna on theground.

Therefore, since the signals A1, A2, B1, and B2 are satellite waves, anda diversity effect can be obtained by the satellites BS1 and BS2, abroadcast can be listened to over the entire U.S. Also, when there is ahigh-rise building, radio waves are sometimes blocked, but this iscompensated for by the signals A3 and B3 of the terrestrial waves.Therefore, even when the receiving conditions of radio waves of areceiver mounted in a vehicle greatly change as the vehicle travels, itis possible to satisfactorily receive a broadcast.

In DARS, since the signals A1 to A3 and B1 to B3 are broadcast byfrequency division in the above-described manner, a receiver therefor isconstructed as shown in, for example, FIG. 7. In the followingdescription, for brevity of explanation, as shown in FIG. 8A, thesignals A1 and A2 are collectively denoted as A12, and the signals B1and B2 are collectively denoted as B12.

More specifically, in FIG. 7, the signals A12, A3, B12, and B3 arereceived by an antenna 11, and the received signals A12 to B3 aresupplied to a first mixer circuit 14 via a band-pass filter 12 and ahigh-frequency amplifier 13. Furthermore, a first local oscillationsignal SLO is supplied from a first local oscillation circuit 15 to thefirst mixer circuit 14, whereby the signals A12 to B3 arefrequency-converted into first intermediate frequency signals.

When the ensemble A is to be listened to (when the signals A1 to A3 aresubjects to be received), as indicated by the solid line in FIG. 8A, thefirst local oscillation signal SLO is set to a predetermined frequencyfL which is lower than those of the signals A12 and A3. Therefore, asshown in FIG. 8B, the signal A12 is frequency-converted into a firstintermediate frequency signal SIF12 (at intermediate frequency fIF12),the signal A3 is frequency-converted into a first intermediate frequencysignal SIF3 (at intermediate frequency fIF3), and the signals B12 and B3are frequency-converted into first intermediate frequency signals SIF45and SIF6, respectively.

When the image rejection characteristics are taken into consideration,the first intermediate frequencies fIF12 and fIF3 cannot be decreasedtoo much, and since a frequency band of 2.3 GHz is used in a broadcast,the first intermediate frequencies fIF12 and fIF3 are set to 100 MHz orhigher. For example, the following are set:

-   -   fIF12 is approximately 113 MHz, and fIF3 is approximately 116        MHz

Also, when the ensemble B is to be listened to (when the signals B1 toB3 are subjects to be received), as indicated by the broken line in FIG.8A, the first local oscillation signal SLO is set to a predeterminedfrequency fH which is higher than those of the signals B12 and B3.Therefore, as shown in FIG. 8C, the signal B12 is frequency-convertedinto a first intermediate frequency signal SIF12 (at intermediatefrequency fIF12), the signal B3 is frequency-converted into a firstintermediate frequency signal SIF3 (at intermediate frequency fIF3), andthe signals A12 and A3 are frequency-converted into first intermediatefrequency signals SIF45 and SIF6, respectively.

Therefore, when any one of the ensembles A and B is to be listened to,the intermediate frequency signals SIF12 to SIF6 are supplied to aband-pass filter 21L for a first intermediate frequency filter, wherebyan intermediate frequency signal SIF12 is extracted. Then, this signalis supplied to a second mixer circuit 22L, a second local oscillationsignal having a predetermined frequency is provided from a second localoscillation circuit 23, and this signal is supplied to the mixer circuit22L, whereby the signal SIF12 is frequency-converted into a secondintermediate frequency signal. Then, this signal is supplied to ademodulation circuit 25L via a variable gain amplifier 24L for AGC(Automatic Gain Control), whereby a digital audio signal of the targetprogram is demodulated, and this signal is supplied to aselecting/combining circuit 26.

Also, the signals SIF12 to SIF6 from the first mixer circuit 14 issupplied to a band-pass filter 21H for a first intermediate frequencyfilter, whereby the intermediate frequency signal SIF3 is extracted.Then, this signal is supplied to a second mixer circuit 22H, andfurthermore, a second local oscillation signal from the second localoscillation circuit 23 is supplied to the mixer circuit 22H, whereby thesignal SIF3 is frequency-converted into a second intermediate frequencysignal. Then, this signal is supplied to a demodulation circuit 25H viaa variable gain amplifier 24H for AGC, whereby a digital audio signal ofthe target program is demodulated, and this signal is supplied to theselecting/combining circuit 26.

Then, in the selecting/combining circuit 26, the signal from thedemodulation circuit 25L and the signal from the demodulation circuit25H are selected or combined, and is output at an output terminal 27.

Therefore, as a result of switching the frequency of the first localoscillation signal SLO to a frequency fL or a frequency fH, a digitalsignal of the ensemble A or a digital signal of the ensemble B is outputat the terminal 27.

Then, at that time, when the ensemble A is received, since the digitalsignal demodulated from the received signal A12 and the digital signaldemodulated from the received signal A3 are selected or combined, and istaken out at the terminal 27, a digital signal having a small amount oferror can be obtained regardless of the receiving conditions.Furthermore, also when the ensemble B is received, a digital signalhaving a small amount of error can be obtained regardless of thereceiving conditions for the same reasons.

However, in the above-described receiver, when the ensemble is switchedfrom the ensemble A to the ensemble B, it is necessary to change thefrequency of the first local oscillation signal SLO from the frequencyfL to the frequency fH. That is, as is also clear from FIGS. 8A to 8C,it is necessary to change the frequency of the first local oscillationsignal SLO to a frequency larger than the occupied bandwidth 12.5 MHz ofthe services of the signals A1 to A3 and B1 to B3. Also, the sameapplies to a case in which the ensemble is changed from the ensemble Bto the ensemble A.

The amount of change of this frequency is equal to or more than 10% ofthe frequencies fL and fH. Moreover, when the first local oscillationcircuit 15 is formed by a PLL (Phase-Locked Loop), it is necessary toallow for some margin with respect to the range of change of theoscillation frequency of the VCO (Voltage Controlled Oscillator) of thePLL. For this reason, it is necessary to increase the range of change ofthe oscillation frequency of the VCO by making the resonance device ofthe VCO changeable. As a result, the construction becomes complex, andthe phase noise characteristics of the local oscillation signal SLOdeteriorate, causing the error rate of the digital signal to becomeworse.

Also, as long as the first local oscillation circuit 15 is formed by aPLL, it takes time to change the frequency, and the ensemble cannot bereceived during that change.

In addition, the first intermediate frequencies fIF12 and fIF3 areincreased to 100 MHz or higher in the above-described manner, and asshown in FIGS. 8B and 8C, it is necessary for the filters 21L and 21H toextract the first intermediate frequency signals SIF12 and SIF3 fromwithin the crowded signals. As a result, the filters 21L and 21H areformed by an SAW (Surface Acoustic Wave) filter. For this reason, thecost increases, and when the circuit is formed into an IC (integratedcircuit), the SAW filter must be provided externally. Furthermore, thisbecomes an obstacle to the reduction in size of the receiver.

Also, when the demodulation of the demodulation circuits 25L and 25H isto be performed by a digital process, an intermediate frequency signalsupplied to the demodulation circuits 25L and 25H must be formed into afrequency at which a digital process is possible. For this purpose, asis also shown in FIG. 7, for the receiving method, a double conversionmethod must be used, the construction becomes complex, and the number ofparts is increased.

SUMMARY OF THE INVENTION

The present invention aims to solve such problems as those describedabove.

Accordingly, an object of the present invention is to provide areceiving device comprising: a receiving circuit for receiving a firstsignal and a second signal which are transmitted at mutually differentfrequencies; a circuit for forming first and second local oscillationsignals, whose frequencies are both the center frequency between thefirst signal and the second signal, and whose phases differ by 90° fromeach other: a first mixer circuit for frequency-converting the receivedsignal received by the receiving circuit into a first intermediatefrequency signal in accordance with the first local oscillation signal;a second mixer circuit for frequency-converting the received signalreceived by the receiving circuit into a second intermediate frequencysignal in accordance with the second local oscillation signal; a firstphase-shift circuit to which the first intermediate frequency signal issupplied; a second phase-shift circuit to which the second intermediatefrequency signal is supplied, in which the amount of the phase shiftdiffers by 90° from that of the first phase-shift circuit; and anaddition/subtraction circuit for performing one of addition andsubtraction between the output signal of the first phase-shift circuitand the output signal of the second phase-shift circuit, wherein, byswitching the process in the addition/subtraction circuit to theaddition or the subtraction, the intermediate frequency signalcorresponding to the first signal or the intermediate frequency signalcorresponding to the second signal is selectively extracted from theaddition/subtraction circuit.

Therefore, while the local oscillation frequency is being fixed, thefirst signal or the second signal is selected.

In particular, a receiving device is provided which is suitable for acase in which each of the first and second signals is formed of a signalof a plurality of programs, and the signals of individual programs aretransmission programs which are arranged according to frequencysymmetrically with respect to the center frequency.

More specifically, when the ensemble is to be switched, since thefrequency of the local oscillation signal does not need to be changed,the local oscillation circuit does not become complex. Also, thedeterioration of the phase noise characteristics of the localoscillation signal, and the deterioration of the error rate of thedigital signal do not occur. Furthermore, when the ensemble is to beswitched, the switching can be performed easily at high speed, and theproblem where the ensemble cannot be received during the switching, likewhen the local oscillation frequency is to be changed, does not occur.

Another object of the present invention is to provide a receptionintegrated circuit which is suitable for constructing theabove-described receiving device. According to the integrated circuit ofthe present invention, in addition to the above-described features, theintermediate-frequency filter can be formed by an active filter, and canbe integrally formed into a one-chip IC with other circuits. This iseffective in reducing the cost and the size of the receiver.Furthermore, even when demodulation is to be performed by a digitalprocess, a single conversion may be used for the receiving method, theconstruction becomes simple, and the number of parts is decreased.

The above and further objects, aspects and novel features of theinvention will become more fully apparent from the following detaileddescription when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of the presentinvention;

FIGS. 2A, 2B, and 2C are frequency spectrum diagrams illustrating thepresent invention;

FIG. 3 is a block diagram showing another embodiment of the presentinvention;

FIG. 4 is a circuit diagram showing a part of the other embodiment ofthe present invention;

FIG. 5 is a circuit diagram showing a part of the other embodiment ofthe present invention;

FIG. 6 is a frequency spectrum diagram illustrating DARS;

FIG. 7 is a block diagram showing the present invention; and

FIGS. 8A, 8B, and 8C are frequency spectrum diagrams illustrating thecircuit of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an example of a DARS receiving circuit according to thepresent invention, in which a portion 30 surrounded by a one-dot chainline is formed into a one-chip IC. Signals A1 to A3, and B1 to B3 arereceived by an antenna 51, and the received signals A1 to B3 aresupplied to mixer circuits 32I and 32Q via a band-pass filter 52, whichis formed of, for example, an SAW filter and which has a passingbandwidth of 12.5 MHz and furthermore via a high-frequency amplifier 31.

In a local oscillation circuit 33, as shown in FIG. 2A, an oscillationsignal SLO having a frequency equal to the center frequency fC betweenthe signal A3 and the signal B3 is formed, this signal SLO is suppliedto a phase processing circuit 34, whereby two local oscillation signalsSLI and SLQ, whose phases differ by 90° from each other, with thefrequency being kept at the value fC, are formed, and these signals SLIand SLQ are supplied to the mixer circuits 32I and 32Q, respectively.

In the following description, for brevity of explanation, it is assumedthat, as shown in FIG. 2A, the signal SA represents each of the signalsA1 to A3, and the signal SB represents each of the signals B1 to B3.That is, it is assumed that SA=A1, SA=A2, or SA=A3, and that SB=B1,SB=B2, or SB=B3. Then, it is arranged that:SA=EA·sin ωAtSB=EB·sin ωBtwhere EA is the amplitude of the signal SA, EB is the amplitude of thesignal SB, ωA is the angular frequency of the signal SA, and ωB is theangular frequency of the signal SB.Also, it is arranged that:SLI=EL·sin ωCtSLQ=EL·cos ωCtwhere EL is the amplitude of the signals SLI and SLQ, and ωC=2πfC.

Then, from the mixer circuits 32I and 32Q, signals SIFI and SIFQ asdescribed below are extracted:SIFI=(SA+SB)×SLI=EA·sin ωAt×EL·sin ωCt+EB·sin ωBt×EL·sin ωCt=α{cos (ωA−ωC)t−cos (ωA+ωC)t}+β{cos (ωB−ωC)t−cos (ωB+ωC)t}SIFQ=(SA+SB)×SLQ=EA·sin ωAt×EL·cos ωCt+EB·sin ωBt×EL·cos ωCt=α{sin (ωA+ωC)t+sin (ωA−ωC)t}+β{sin (ωB+ωC)t+sin (ωB−ωC)t}where α=EA·EL/2, and β=EB·EL/2

As will be described later, of the signals SIFI and SIFQ, the signalcomponents of angular frequencies (ωA−ωC) and (ωB−ωC) are used as theintermediate frequency signals, and the signal components of angularfrequencies (ωA+ωC) and (ωB+ωC) are removed by the intermediatefrequency filter. Therefore, for the sake of simplicity, if the signalcomponents of angular frequencies (ωA+ωC) and (ωB+ωC) to be removed areignored, the above equations become:SIFI=α·cos(ωA−C)t+β·cos(ωB−C)tSIFQ=α·sin(ωA−C)t+β·sin(ωB−C)t

Here, if it is arranged that ωA=ωC−Δω with regard to the signal SA,since, as is also shown in FIG. 2A, the signal SA and the signal SB aresymmetrically distributed about the frequency fC, the following equationholds:ωB=ωC+αω

Then, if these equations are substituted in the equations for thesignals SIFI and SIFQ, the following equations are obtained:SIFI=α·cos(ωC−Δω−ωC)t+β·cos(ωC+Δω−ωC)t=α·cos(−Δω)t+β·cos Δωt=α·cos Δωt+β·cos ΔωtSIFQ=α·sin(ωC−Δω−ωC)t+β·sin(ωC+Δω−C)t=α·sin(−Δω)t+β·sin Δωt=α·sin Δωt+β·sin Δωt

These signals SIFI and SIFQ are then supplied to phase-shift circuits35I and 35Q. The phase-shift circuits 35I and 35Q are formed by anactive filter in which, for example, a capacitor, a resistor, and anoperational amplifier are used. The phase-shift circuit 35I phase-shiftsthe signal SIFI by a value φ (φ is an arbitrary value), and thephase-shift circuit 35Q phase-shifts the signal SIFQ by a value (φ+90°).

In this manner, the phase-shift circuits 35I and 35Q cause the signalSIFQ to lead the signal SIFI by 90°, and the following equations hold:SIFI=α·cos Δωt+β·cos ΔωtSIFQ=−α·sin(Δωt+90°)+β·sin(Δωt+90°)=−α·cos Δωt+β·cos ΔωtTherefore, between the signal SIFI and the signal SIFQ, the signalcomponents α·cos Δωt are at the opposite phase from each other, and thesignal components β·cos Δωt are in phase.

These signals SIFI and SIFQ are then supplied to an addition/subtractioncircuit 36, and a control signal SSW is supplied from a terminal 37 tothe addition/subtraction circuit 36. This control signal SSW controlsthe operation of the addition/subtraction circuit 36 in such a way thatwhen the program of the ensemble A is to be listened to, theaddition/subtraction circuit 36 acts as a subtraction circuit, and whenthe program of the ensemble B is to be listened to, theaddition/subtraction circuit 36 acts as an addition circuit.

Therefore, a signal SIF such as that described below is extracted fromthe addition/subtraction circuit 36 in such a manner as to correspond tothe control signal SSW. That is, during subtraction, the following isextracted:SIF=SIFI−SIFQ=2αcos Δωt=EL·EA·cos Δωt,and during addition, the following is extracted:SIF=SIFI+SIFQ=2β·cos Δωt=EL·EB·cos Δωt

Here, the signal SIF=EL·EA·cos Δωt which is obtained during subtractionis, as is also shown in FIG. 2B, the same intermediate frequency signalwhen the signal SA is received. The signals SIF1 to SIF3 contained inthis signal SIF are the intermediate frequency signals of the signals A1to A3. Also, the signal SIF=EL·EB·cos Δωt which is obtained duringaddition is, as is also shown in FIG. 2C, the same intermediatefrequency signal when the signal SB is received. The signals SIF1 toSIF3 contained in this signal SIF are the intermediate frequency signalsof the signals B1 to B3.

Therefore, this signal SIF is supplied to a band-pass filter 41H for anintermediate-frequency filter having passing characteristics such asthose indicated by the broken line in, for example, FIGS. 2B and 2C,whereby an intermediate frequency signal SIF3 of a terrestrial-wavesignal A3 or B3 is extracted. At this time, the intermediate frequencysignals SIF1 and SIF2 and the above-mentioned signal components ofangular frequencies (ωA+ωC) and (ωB+ωC) are removed by the band-passfilter 41H.

Then, this intermediate frequency signal SIF3 is supplied to ademodulation circuit 43H via a variable gain amplifier 42H for AGC,whereby a digital audio signal of the target program is demodulated, andthis signal is supplied to a selecting/combining circuit 44.

Also, the signal SIF from the addition/subtraction circuit 36 issupplied to a band-pass filter 41L for an intermediate-frequency filterhaving passing characteristics such as those indicated by the brokenline in, for example, FIGS. 2B and 2C, whereby intermediate frequencysignals SIF2 and SIF1 of the satellite-wave signals A1 and A2, or B1 andB2 are extracted. At this time, the intermediate frequency signal SIF3and the above-mentioned signal components of angular frequencies (ωA+ωC)and (ωB+ωC) are removed by the filter 41L.

Then, these intermediate frequency signals SIF2 and SIF1 are supplied toa demodulation circuit 43L via a variable gain amplifier 42L for AGC,whereby a digital audio signal of the target program is demodulated, andthis signal is supplied to the selecting/combining circuit 44.

Then, in the selecting/combining circuit 44, the digital signal from thedemodulation circuit 43H and the digital signal from the demodulationcircuit 43L are selected or combined according to the received status ofthe signals A1 to B3, and is extracted at an output terminal 45. Ofcourse, when it is desired to give priority to a receiving environmentof a mobile unit in which the receiver is mounted and to satellite-wavereception, the AGC voltage obtained from the level detection circuit 46Lmay be supplied as a gain control signal.

At this time, parts of the intermediate frequency signals from thedemodulation circuits 43H and 43L are supplied to level detectioncircuits 46H and 46L, whereby AGC voltages are formed, and these AGCvoltages are supplied, as gain control signals, to the amplifiers 42Hand 42L, whereby AGC is performed.

In addition, although the level variation of the satellite wave isrelatively small, the level variation of the terrestrial wave isrelatively large. Therefore, for the high-frequency amplifier 31, avariable gain amplifier is used, and the AGC voltage obtained from thelevel detection circuit 46H is supplied, as a gain control signal, tothe amplifier 31, whereby AGC is performed.

In this manner, according to the receiving circuit of FIG. 1, abroadcast by DARS can be received, and in a case where the ensemble isswitched between the ensemble A and the ensemble B, the frequency fC ofthe local oscillation signals SLI and SLQ does not need to be changed.Consequently, the local oscillation circuit 33 may be formed in astandard construction and does not become complex. Also, since the phasenoise characteristics of the local oscillation signals SLI and SLQ arenot decreased, the error rate of the digital signal does not becomeworse.

In addition, when the ensemble is to be switched, theaddition/subtraction circuit 36 need only be switched to an additionoperation or a subtraction operation. Consequently, the switching can beperformed at high speed, and the problem of not being able to receivethe ensemble during switching time does not occur.

As is also clear from FIGS. 2B and 2C, since the upper-limit frequencyof the occupied bandwidth of the intermediate frequency signal SIF isequal to a half of the bandwidth of one ensemble, and the centerfrequencies of the filters 41H and 41L become approximately 1.3 MHz and4.4 MHz, it is possible to form each of the filters 41H and 41L by anactive filter. Therefore, it is possible to form the entirety into aone-chip IC as an IC 30, excluding a band-pass filter 52 at the antennainput stage, and this is effective in reducing the costs and the size ofthe receiver.

In addition, since the intermediate frequency of the intermediatefrequency signals SIF3 to SIF1 is as low as several MHz, even when thedemodulation of the demodulation circuits 43H and 43L is performed by adigital process, as shown in, for example, FIG. 1, for the receivingmethod, a single conversion may be used, the construction becomessimple, and the number of parts is decreased.

In the receiving circuit shown in FIG. 3, a case is shown in which, byinverting or non-inverting the phase of the local oscillation signal SLQwhen the ensemble A is received and when the ensemble B is received, thesignals SIFI and SIFQ are always added together.

More specifically, in the receiving circuit in FIG. 3, the controlsignal SSW is supplied as a phase control signal to the phase processingcircuit 34, so that the phase of the local oscillation signal SLQ iscontrolled such that:

SLQ=+EL·cos ωCt . . . when the ensemble B is received, and

SLQ=−EL·cos ωCt . . . when the ensemble A is received.

The phase of the local oscillation signal SLI is fixed, as describedabove:

SLI=EL·sin ωCt

In place of the addition/subtraction circuit 36 in FIG. 1, an additioncircuit 38 is provided, and the signals SIFI and SIFQ output from thephase-shift circuits 35I and 35Q are supplied to the addition circuit38.

According to such a construction, in the case of SLQ=+EL·cos ωCt, in theaddition circuit 38, the signal SIFI and the signal SIFQ are addedtogether. Therefore, as is described with reference to the receivingcircuit of FIG. 1, the signal SIF extracted from the addition circuit 38becomes as follows:SIF=SIFI+SIFQ=EL·EB·cos ΔωtTherefore, it is possible to listen to the program of the ensemble B.

On the other hand, in the case of SLQ=−EL·cos ωCt, the output signal ofthe phase-shift circuit 35Q becomes the signal −SIFQ. Therefore, since,in the addition circuit 38, subtraction between the signal SIFI and thesignal SIFQ is performed, as is described with reference to thereceiving circuit of FIG. 1, the signal SIF extracted from the additioncircuit 38 becomes:SIF=SIFI−SIFQ=EL·EA·cos ΔωtTherefore, it is possible to listen to the program of the ensemble A.

In this way, also in the receiving circuit of FIG. 3, a DARS broadcastcan be received. In particular, according to the receiving circuit ofFIG. 3, in a case where the ensemble is switched between the ensemble Aand the ensemble B, it is only necessary to invert or non-invert thephase of the local oscillation signal SLQ by the phase processingcircuit 34. Therefore, the ensemble can be switched quickly. Also, sincethe phase-shift circuits 35I and 35Q and the addition circuit 38 can beformed by a poly-phase filter, the phase characteristics of the signalSIFI and the signal ±SIFQ can be improved.

In FIG. 4, a case is shown in which the phase of the intermediatefrequency signal SIFI is constant regardless of the ensemble which isreceived, but the phase of the intermediate frequency signal SIFQ isinverted or non-inverted between when the ensemble A is to be receivedand when the ensemble B is to be received.

More specifically, the mixer circuit 32Q is formed as a doublebalanced-type by transistors Q321 to Q327. The received signals A1 to A3and B1 to B3 are extracted as a balanced type from the amplifier 31 andare supplied to transistors Q322 and Q323. Furthermore, the localoscillation signal SLQ is extracted as a balanced type from the phaseprocessing circuit 34 and is supplied to transistors Q324, Q327, Q325,and Q326.

Consequently, the intermediate frequency signal SIFQ is extracted as abalanced type from the mixer circuit 32Q. That is, for example, theintermediate frequency signal +SIFQ is extracted from the transistorsQ324 and Q326, and the intermediate frequency signal −SIFQ is extractedfrom the transistors Q325 and Q327.

Then, these intermediate frequency signal ±SIFQ are supplied to aswitching circuit 39. This switching circuit 39 is formed as a balancedtype by transistors Q391 to Q397, and the intermediate frequency signals±SIFQ which are supplied thereto are supplied to a phase-shift circuit36Q in accordance with the control signal SSW with the phase kept as itis or with the phase being inverted.

More specifically, based on the control signal SSW, when the transistorQ395 is on and transistor Q396 is off, the transistors Q392 and Q393 areturned on, and the transistors Q391 and Q394 are turned off. Therefore,the intermediate frequency signal +SIFQ extracted from the transistorsQ324 and Q326 is supplied to one of the balance input terminals of thephase-shift circuit 36Q via the transistor Q392. Also, the intermediatefrequency signal −SIFQ extracted from the transistors Q325 and Q327 issupplied to the other one of the balance input terminals of thephase-shift circuit 36Q via the transistor Q393.

However, based on the control signal SSW, when the transistor Q396 is onand the transistor Q395 is off, the transistors Q391 and Q394 are turnedon, and the transistors Q392 and Q393 are turned off. Therefore, theintermediate frequency signal +SIFQ extracted from the transistors Q324and Q326 is supplied to the other one of the balance input terminals ofthe phase-shift circuit 36Q via the transistor Q391. Also, theintermediate frequency signal −SIFQ extracted from the transistors Q325and Q327 is supplied to one of the balance input terminals of thephase-shift circuit 36Q via the transistor Q394.

Therefore, since the phase of the intermediate frequency signal SIFQsupplied to the phase-shift circuit 36Q is inverted or non-inverted inaccordance with the control signal SSW, the intermediate frequencysignal SIF of the ensemble A or the ensemble B is output from theaddition circuit 38. In this case, since the phase of the intermediatefrequency signal SIFQ need only be inverted or non-inverted by theswitching circuit 39, it is possible to quickly switch the ensemble.

Although the phase of the intermediate frequency signal SIFI is keptfixed, the intermediate frequency signal SIFI output from the mixercircuit 32I may be supplied to a phase-shift circuit 36I via a switchingcircuit having the same construction as that of the switching circuit39, and the switching circuit may be kept fixed.

FIG. 5 shows a circuit 34Q of a portion which switches the phase of thelocal oscillation signal SLQ within the phase processing circuit 34 inFIG. 3. That is, the mixer circuit 32Q is formed as a doublebalance-type as described in FIG. 4, and the received signals A1 to A3and B1 to B3 are extracted as a balanced type and are supplied to thetransistors Q322 and Q323.

Furthermore, the switching circuit 34Q is formed as a doublebalanced-type by the transistors Q341 to Q347. The local oscillationsignal +SLQ of one of the phases is supplied to the transistors Q345 andQ346, and the local oscillation signal −SLQ of the other phases issupplied to the transistors Q344 and Q347. Also, the balanced-typecontrol signal SSW is supplied to the transistors Q342 and Q343.

Then, based on the control signal SSW, when the transistor Q342 is onand the transistor Q343 is off, the transistors Q344 and Q345 are turnedon, and the transistors Q346 and Q347 are turned off. Therefore, thelocal oscillation signal +SLQ is supplied to the transistors Q324 toQ327 via the transistor Q345 and further via the emitter-followertransistor Q349. Also, the local oscillation signal −SLQ is supplied tothe transistors Q325 and Q326 via the transistor Q344 and further viathe emitter-follower transistor Q348.

However, based on the control signal SSW, when the transistor Q343 is onand the transistor Q342 is off, the transistors Q346 and Q347 are turnedon, and the transistors Q344 and Q345 are turned off. Therefore, thelocal oscillation signal +SLQ is supplied to the transistors Q325 andQ326 via the transistor Q346 and further via the transistor Q348. Also,the local oscillation signal −SLQ is supplied to the transistors Q324and Q327 via the transistor Q347 and further via the transistor Q349.

Therefore, since the phase of the local oscillation signal SLQ suppliedto the mixer circuit 32Q is made to lead or reversed in accordance withthe control signal SSW, the intermediate frequency signal SIF of theensemble A or the ensemble B is output from the addition circuit 38.Also in this case, since the phase of the local oscillation signal SLQneed only be inverted or non-inverted by the switching circuit 34Q, theensemble can be switched quickly.

Many different embodiments of the present invention may be constructedwithout departing from the spirit and scope of the present invention. Itshould be understood that the present invention is not limited to thespecific embodiments described in this specification. To the contrary,the present invention is intended to cover various modifications andequivalent arrangements included within the spirit and scope of theinvention as hereafter claimed. The scope of the following claims is tobe accorded the broadest interpretation so as to encompass all suchmodifications, equivalent structures and functions.

1. A receiving device comprising: a receiving circuit for receiving afirst signal and a second signal transmitted at mutually differentfrequencies; a circuit for forming first and second local oscillationsignals having frequencies at a center frequency between said firstsignal and said second signal and having phases that differ by 90° fromeach other; a first mixer circuit for frequency-converting a receivedsignal received by said receiving circuit into a first intermediatefrequency signal in accordance with said first local oscillation signal;a second mixer circuit for frequency-converting the received signalreceived by said receiving circuit into a second intermediate frequencysignal in accordance with said second local oscillation signal; a firstphase-shift circuit to which said first intermediate frequency signal issupplied; a second phase-shift circuit to which said second intermediatefrequency signal is supplied, in which the amount of phase shift in saidsecond phase-shift circuit differs by 90° from an amount of phase shiftof said first phase-shift circuit; and an addition/subtraction circuitfor switchably performing one of addition and subtraction between anoutput signal of said first phase-shift circuit and an output signal ofsaid second phase-shift circuit, wherein, by switching saidaddition/subtraction circuit to perform addition or subtraction, theintermediate frequency signal corresponding to said first signal or theintermediate frequency signal corresponding to said second signal isselectively extracted from said addition/subtraction circuit.
 2. Areceiving device for receiving a multiplexed signal in which a firstensemble having signals of a first plurality of programs and a secondensemble having signals of a second plurality of programs arefrequency-multiplexed and transmitted and for extracting from themultiplexed received signal one of the signals within said signals ofthe first plurality of programs and said signals of the second pluralityof programs, said receiving device comprising: a circuit for formingfirst and second local oscillation signals having frequencies at acenter frequency between said first ensemble and said second ensembleand having phases that differ by 90° from each other; a first mixercircuit for frequency-converting said received signal into a firstintermediate frequency signal in accordance with said first localoscillation signal; a second mixer circuit for frequency-converting thereceived signal into a second intermediate frequency signal inaccordance with said second local oscillation signal; a firstphase-shift circuit to which said first intermediate frequency signal issupplied; a second phase-shift circuit to which said second intermediatefrequency signal is supplied, in which the amount of phase shift in saidsecond phase-shift circuit differs by 90° from an amount of phase-shiftof said first phase-shift circuit; and an addition/subtraction circuitfor switchably performing one of addition and subtraction between anoutput signal of said first phase-shift circuit and an output signal ofsaid second phase-shift circuit, wherein, by switching saidaddition/subtraction circuit to perform addition or subtraction, thefirst intermediate frequency signal or the second intermediate frequencysignal is selectively extracted from said addition/subtraction circuit.3. The receiving device according to claim 2, further comprising: anintermediate frequency filter to which the output signal of saidaddition/subtraction circuit is supplied; and a demodulation circuit towhich an output signal of the intermediate frequency filter is supplied,wherein, by switching said addition/subtraction circuit to performaddition or subtraction, the signals of said first plurality of programsor the signals of said second plurality of programs are selectivelyextracted from said demodulation circuit.
 4. The receiving deviceaccording to claim 3, wherein, when each of said first ensemble and saidsecond ensemble has a terrestrial-wave signal and a satellite-wavesignal which are frequency-divided, said intermediate frequency filtercomprises first and second intermediate frequency filters, saiddemodulation circuit comprises first and second demodulation circuits,the output signal of said addition/subtraction circuit is supplied toeach of said first and second intermediate frequency filters, wherebythe intermediate frequency signal of said terrestrial-wave signal andthe intermediate frequency signal of said satellite-wave signal areextracted from said first and second intermediate frequency filters, andthe intermediate frequency signals output from said first and secondintermediate frequency filters are supplied to said first and seconddemodulation circuits, respectively.
 5. A receiving device comprising: areceiving circuit for receiving a first signal and a second signaltransmitted at mutually different frequencies; a circuit for formingfirst and second local oscillation signals having frequencies at acenter frequency between said first signal and said second signal andhaving phases that differ by 90° from each other; a first mixer circuitfor frequency-converting the received signal received by said receivingcircuit into a first intermediate frequency signal in accordance withsaid first local oscillation signal; a second mixer circuit forfrequency-converting the received signal received by said receivingcircuit into a second intermediate frequency signal in accordance withsaid second local oscillation signal; a first phase-shift circuit towhich said first intermediate frequency signal is supplied; a secondphase-shift circuit to which said second intermediate frequency signalis supplied, in which the amount of phase shift in said secondphase-shift circuit differs by 90° from an amount of phase shift of saidfirst phase-shift circuit; and an addition circuit for performingaddition of the output signal of said first phase-shift circuit and theoutput signal of said second phase-shift circuit; and a circuit forselectively inverting or non-inverting the phase of one of the outputsignal of said first phase-shift circuit and the output signal of saidsecond phase-shift circuit supplied to said addition circuit, wherein,by switching between said inverting or said non-inverting, theintermediate frequency signal corresponding to said first signal or theintermediate frequency signal corresponding to said second signal isselectively extracted from said addition circuit.
 6. The receivingdevice according to claim 5, wherein said circuit for selectivelyinverting or non-inverting is a circuit for inverting or non-invertingthe phase of one of the signals of said first and second localoscillation signals.
 7. The receiving device according to claim 5,wherein said circuit for selectively inverting or non-inverting is acircuit for inverting or non-inverting the phase of one of the signalsof said first and second intermediate frequency signals.
 8. A receivingdevice for receiving a multiplexed signal in which a first ensemblehaving signals of a first plurality of programs and a second ensemblehaving signals of a second plurality of programs arefrequency-multiplexed and transmitted and for extracting from themultiplexed received signal one of the signals within said signals ofthe first plurality of programs and said signals of the second pluralityof programs, said receiving device comprising: a circuit for formingfirst and second local oscillation signals having frequencies at acenter frequency between said first ensemble and said second ensembleand having phases that differ by 90° from each other; a first mixercircuit for frequency-converting the received signal into a firstintermediate frequency signal in accordance with said first localoscillation signal; a second mixer circuit for frequency-converting thereceived signal into a second intermediate frequency signal inaccordance with said second local oscillation signal; a firstphase-shift circuit to which said first intermediate frequency signal issupplied; a second phase-shift circuit to which said second intermediatefrequency signal is supplied, in which an amount of in said secondphase-shift circuit phase shift differs by 90° from an amount of phaseshift of said first phase-shift circuit; an addition circuit forperforming addition of the output signal of said first phase-shiftcircuit and the output signal of said second phase-shift circuit; and acircuit for selectively inverting or non-inverting the phase of one ofsaid first and second intermediate frequency signals, wherein, byswitching between said inverting or said non-inverting, the intermediatefrequency signal corresponding to said first signal or the intermediatefrequency signal corresponding to said second signal is selectivelyextracted from said addition circuit.
 9. The receiving device accordingto claim 8, further comprising: an intermediate frequency filter towhich the output signal of said addition circuit is supplied; and ademodulation circuit to which an output signal of the intermediatefrequency filter is supplied, wherein, by switching between saidinverting or said non-inverting, the signals of said first plurality ofprograms or the signals of said second plurality of programs areselectively extracted from said demodulation circuit.
 10. The receivingdevice according to claim 9, wherein, when each of said first ensembleand said second ensemble has a terrestrial-wave signal and asatellite-wave signal which are frequency-divided, said intermediatefrequency filter comprises first and second intermediate frequencyfilters, said demodulation circuit comprises first and seconddemodulation circuits, the output signal of said addition circuit issupplied to each of said first and second intermediate frequencyfilters, whereby the intermediate frequency signal of saidterrestrial-wave signal and the intermediate frequency signal of saidsatellite-wave signal are extracted from said first and secondintermediate frequency filters, and the intermediate frequency signalsoutput from said first and second intermediate frequency filters aresupplied to said first and second demodulation circuits, respectively.11. The receiving device according to claim 10, further comprising aselecting/combining circuit for selecting or combining the demodulatedoutputs of said first and second demodulation circuits and foroutputting the demodulated outputs.
 12. The receiving device accordingto claim 8, wherein said circuit for selectively inverting ornon-inverting is a circuit for inverting or non-inverting the phase ofone of the signals of said first and second local oscillation signals.13. The receiving device according to claim 8, wherein said circuit forselectively inverting or non-inverting is a circuit for inverting ornon-inverting the phase of one of the signals of said first and secondintermediate frequency signals.
 14. An integrated circuit for receptioncomprising: a high-frequency amplifier for receiving a first signal anda second signal transmitted at mutually different frequencies; a circuitfor forming first and second local oscillation signals havingfrequencies at a center frequency between said first signal and saidsecond signal, and having phases that differ by 90° from each other; afirst mixer circuit for frequency-converting the received signalreceived by said high-frequency amplifier into a first intermediatefrequency signal in accordance with said first local oscillation signal;a second mixer circuit for frequency-converting the received signalreceived by said high-frequency amplifier into a second intermediatefrequency signal in accordance with said second local oscillationsignal; a first phase-shift circuit to which said first intermediatefrequency signal is supplied; a second phase-shift circuit to which saidsecond intermediate frequency signal is supplied, in which an amount ofphase shift in said second phase-shift circuit differs by 90° from anamount of phase-shift of said first phase-shift circuit; and anaddition/subtraction circuit for switchably performing one of additionand subtraction between an output signal of said first phase-shiftcircuit and an output signal of said second phase-shift circuit, whichare integrated into one chip, wherein, by switching saidaddition/subtraction circuit to perform addition or subtraction, theintermediate frequency signal corresponding to said first signal or theintermediate frequency signal corresponding to said second signal isselectively extracted from said addition/subtraction circuit.
 15. Areception integrated circuit for receiving a multiplexed signal in whicha first ensemble having signals of a first plurality of programs and asecond ensemble having signals of a second plurality of programs arefrequency-multiplexed and transmitted and for extracting from themultiplexed received signal one of the signals within the signals ofsaid first plurality of programs and the signals of said secondplurality of programs, said reception integrated circuit comprising: acircuit for forming first and second local oscillation signals havingfrequencies at a center frequency between said first ensemble and saidsecond ensemble and having phases that differ by 90° from each other; afirst mixer circuit for frequency-converting the received signal into afirst intermediate frequency signal in accordance with said first localoscillation signal; a second mixer circuit for frequency-converting thereceived signal into a second intermediate frequency signal inaccordance with said second local oscillation signal; a firstphase-shift circuit to which said first intermediate frequency signal issupplied; a second phase-shift circuit to which said second intermediatefrequency signal is supplied, in which an amount of phase shift in saidsecond phase-shift circuit differs by 90° from that an amount of phaseshift of said first phase-shift circuit; an addition/subtraction circuitfor switchably performing one of addition and subtraction between theoutput signal of said first phase-shift circuit and the output signal ofsaid second phase-shift circuit; an intermediate frequency filter towhich an output signal of the addition/subtraction circuit is supplied;and a demodulation circuit to which an output signal of the intermediatefrequency filter is supplied, wherein, by switching saidaddition/subtraction circuit to perform addition or subtraction, thesignals of said first plurality of programs or the signals of saidsecond plurality of programs are selectively extracted from saiddemodulation circuit.
 16. A reception integrated circuit comprising: ahigh-frequency amplifier for receiving a first signal and a secondsignal transmitted at mutually different frequencies; a circuit forforming first and second local oscillation signals having frequencies ata center frequency between said first signal and said second signal, andhaving phases that differ by 90° from each other; a first mixer circuitfor frequency-converting the received signal received by saidhigh-frequency amplifier into a first intermediate frequency signal inaccordance with said first local oscillation signal; a second mixercircuit for frequency-converting the received signal received by saidhigh-frequency amplifier into a second intermediate frequency signal inaccordance with said second local oscillation signal; a firstphase-shift circuit to which said first intermediate frequency signal issupplied; a second phase-shift circuit to which said second intermediatefrequency signal is supplied, in which an amount of phase shift in saidsecond phase-shift circuit differs by 90° from an amount of phase-shiftof said first phase-shift circuit; an addition circuit for performingaddition of the output signal of said first phase-shift circuit and theoutput signal of said second phase-shift circuit; and a circuit forswitchably inverting or non-inverting the phase of one of the outputsignal of said first phase-shift circuit and the output signal of saidsecond phase-shift circuit supplied to said addition circuit, which areintegrated into one chip, wherein, by switching between said invertingor said non-inverting, the intermediate frequency signal correspondingto said first signal or the intermediate frequency signal correspondingto said second signal is selectively extracted from said additioncircuit.
 17. A reception integrated circuit for receiving a multiplexedsignal in which a first ensemble having signals of a first plurality ofprograms and a second ensemble having signals of a second plurality ofprograms are frequency-multiplexed and transmitted and for extractingfrom the multiplexed received signal one of the signals within thesignals of said first plurality of programs and the signals of saidsecond plurality of programs, said reception integrated circuitcomprising: a circuit for forming first and second local oscillationsignals having frequencies at a center frequency between said firstensemble and said second ensemble and having phases that differ by 90°from each other; a first mixer circuit for frequency converting thereceived signal into a first intermediate frequency signal in accordancewith said first local oscillation signal; a second mixer circuit forfrequency-converting the received signal into a second intermediatefrequency signal in accordance with said second local oscillationsignal; a first phase-shift circuit to which said first intermediatefrequency signal is supplied; a second phase-shift circuit to which saidsecond intermediate frequency signal is supplied, in which an amount ofphase shift in said second phase-shift circuit differs by 90° from anamount of phase-shift of said first phase-shift circuit; an additioncircuit for performing addition of an output signal of said firstphase-shift circuit and an output signal of said second phase-shiftcircuit; an intermediate frequency filter to which an output signal ofthe addition circuit is supplied; a demodulation circuit to which theoutput signal of an intermediate frequency filter is supplied; and acircuit for selectively inverting or non-inverting the phase of one ofthe output signal of said first phase-shift circuit and the outputsignal of said second phase-shift circuit supplied to said additioncircuit, which are integrated into one chip, wherein, by switchingbetween said inverting or said non-inverting, the signals of said firstplurality of programs and the signals of said second plurality ofprograms are selectively extracted from said demodulation circuit.